IGBT assembly having saturable inductor for soft landing a diode recovery current
A combination switch includes an Insulated Gate Bipolar Transistor (IGBT), an anti-parallel diode, and a saturable inductor. The diode and inductor are coupled in series between a collector and an emitter of the IGBT. The inductor is fashioned so that it will come out of saturation when a forward bias current flow through the diode falls below a saturation current level. When the diode current falls (for example, due to another combination switch of a phase leg turning on), the diode current initially falls at a high rate until the inductor current drops to the saturation current level. Thereafter, the diode current falls at a lower rate. The lower rate allows the diode current to have a soft landing to zero current, thereby eliminating or reducing voltage and/or current spikes that would otherwise occur. Multiple methods of implementing and manufacturing the saturable inductor are disclosed.
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The described embodiments relate to Insulated Gate Bipolar Transistors (IGBTs).
BACKGROUND INFORMATIONThe combination of an Insulated Gate Bipolar Transistor (IGBT) and an anti-parallel diode is a circuit that sees use in many power electronics circuits. The diode often used is referred to as a Fast Recovery Diode (FRD) or a Fast Recovery Epitaxial Diode (FRED). The diode is coupled between the collector and the emitter of the IGBT in the anti-parallel direction. The IGBT may be a Punch Through type IGBT (PT IGBT) or a Non-Punch Through type IGBT (NPT IGBT).
The three windings of a motor 13 are coupled to the corresponding three output nodes r, g and b of the three legs. The gates of the IGBTs are driven as known in the art to rotate the motor as desired. The ON/OFF duty cycles of the IGBTs determine the time averaged voltages at the output nodes r, g and b. In order to prevent the circuit from generating audible noise, the switching frequency of the IGBTs is generally made to be higher than 15 kHz. In many cases, the motor windings are so highly inductive that the output currents change very slowly compared to the >15 kHz switching frequency. The motor load on a leg can therefore be considered to be a constant current source as compared to the switching on and off of the IGBT.
The rapid decrease in the current in the upper leg can result in a corresponding voltage spike across the upper IGBT as indicated by the upper waveform. If the decrease in diode current in the upper leg is rapid enough, then the voltage drop across the upper diode 20 may be so large that diode 20 will experience avalanche breakdown. In the diagram of
A combination switch includes a Punch Through type Insulated Gate Bipolar Transistor (PT IGBT), an anti-parallel diode, and a saturable inductor. The diode and saturable inductor are coupled in series in a current path between a collector electrode of the IGBT and an emitter electrode of the IGBT. In one example, the IGBT and the diode are mounted directly on a heat sink portion of a stamped metal lead frame. The saturable inductor is disposed on the diode. An emitter lead is wire bonded to the saturable inductor and to an emitter electrode of the IGBT. A gate lead is wire bonded to a gate electrode of the IGBT. The IGBT, the diode, the saturable inductor, and the wire bonds are overmolded with an amount′ of encapsulant, thereby forming a packaged IGBT electronic device. The combination switch can be assembled and packaged in this way as a single combination switch, or as one of a pair of combination switches in the form of a phase leg, or as part of a larger electronic device.
In one example, the IGBT has a maximum continuous collector-to-emitter current. The saturable inductor is sized and fashioned so that it will come out of saturation when current flow through the saturable inductor falls to a saturation current level. This saturation current level is substantially smaller than (for example, less than half of) the maximum continuous collector-to-emitter current and is preferably a current level slightly above zero amperes. In some examples, however, the saturation current level is a current level that is slightly below zero amperes.
In an application where the combination switch is used as the upper combination switch in a phase leg along with another identical combination switch (the lower combination switch), the lower combination switch may initially be off and not conducting current. During this time, a current may flow from an output node of the phase leg, and then through the forward biased diode of the upper combination switch. When the lower combination switch is then made to turn on, the current flow through the forward biased diode of the upper combination switch decreases. This current decreases during a first period of time at a first relatively rapid rate (a relatively large negative dI/dt) until the current flow through the saturable inductor has dropped to the saturation current level. When the current level has dropped to the saturation current level, then the saturable inductor comes out of saturation. The inductance of the saturable inductor increases due to the saturable inductor no longer being saturated, and the subsequent decrease of diode current proceeds during a second period of time at a second relatively smaller rate (a relatively small negative dI/dt). The decreased rate of diode current flow during this second period of time allows the diode current to have what is referred to here as a “soft landing” to zero amperes. The soft landing reduces or eliminates high voltage and current spikes that would otherwise occur if a conventional combination switch were used for the combination switches of the leg.
There are many ways that the saturable inductor of the combination switch can be realized. In a first example, the saturable inductor is a surface mountable wound inductor structure that is mounted on top of the diode integrated circuit. A bottom conductive layer of the inductor structure is solder-mounted to the planar top of the underlying diode integrated circuit. An upper conductive layer of the inductor structure is wire bonded to the emitter lead of the packaged device. The surface mount inductor structure can be a toroidal inductor. In a second example, the saturable inductor is formed by depositing a volume of a liquid bonding agent so that the bonding agent surrounds the emitter bond wire at the location where the emitter bond wire attaches to the top of the diode integrated circuit. The volume of liquid bonding agent contains an amount of ferromagnetic particles. The liquid bonding agent then solidifies to form an inductor structure in which the ferromagnetic particles are held in place with respect to the emitter bond wire by the solidified bonding agent. The emitter bond wire and the solidified bonding agent containing ferromagnetic particles together form the saturable inductor. The method of making an inductor using a volume of curable liquid bonding agent and ferromagnetic particles sees special use in making IGBT electronic devices, but is also of general utility in the electronic arts outside the fields of IGBTs and power electronics.
Further details and embodiments and techniques are described in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims.
The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention.
Reference will now be made in detail to background examples and some embodiments of the invention, examples of which are illustrated in the accompanying drawings.
One of the combination switches of each leg is for coupling an output node of the leg to the first DC voltage conductor 65, whereas the other combination switch of the leg is for coupling the output node of the leg to the second DC voltage conductor 66. Leg 62 includes combination switches 50 and 68. Leg 63 includes combination switches 69 and 70. Leg 64 includes combination switches 71 and 72. The IGBTs are designated with reference numerals 51 and 73-77. The diodes are designated with reference numerals 52 and 78-82. The saturable inductors are designated with reference numerals 53 and 83-87.
Three windings 88-90 of a motor 91 are coupled to the corresponding three output nodes r, g and b of the three legs 62, 63 and 64, respectively. The gates of the IGBTs are driven by control circuitry (not shown) as known in the art to rotate the motor as desired. The ON/OFF duty cycles of the IGBTs determine the time averaged voltages at the output nodes r, g and b. In order to prevent the motor drive circuit 61 from generating audible noise, the switching frequency of the IGBTs is generally made to be higher than 15 kHz. In many cases, the windings of the motor are so highly inductive that the current flows into and out of the output nodes of the legs change very slowly compared to the >15 kHz switching frequency.
Next, as indicated in
Next, as illustrated in
In the case of the novel circuit of
The diagram of
There are numerous ways of implementing a suitable saturable inductor 53.
In some examples, the IGBT and diode integrated circuit dice 121 and 122 are disposed on a thin heat-conductive intervening insulating layer (not shown) that in turn is disposed on heat sink portion 117. The collector lead 119 is not an extension of the heat sink portion 117 but rather is a separate lead. The metal of the heat sink portion 117 is electrically isolated from the IGBT and diode integrated circuits 121 and 122 and from leads 118-120.
Although the method of manufacturing an inductor by depositing an amount of liquid containing ferromagnetic particles is described above in connection with an IGBT circuit, the method of manufacture sees general applicability in the field of electronics. The method is not limited to use in power electronics nor is the amount of deposited ferromagnetic particles restricted to any range or volume. In some examples of the method, a small volume of curable liquid containing ferromagnetic particles is deposited on an electronic device assembly as part of a microdrop of fluid using an automated pick and place assembly device that controls a suitable micro-valve and micro-nozzle. The pick and place assembly device that deposits the microdrop is the same pick and place device that places the other electronic components of the electronic assembly device onto a substrate. The amount of curable liquid deposited by the pick and place machine can be varied from inductor structure to inductor structure where multiple such inductor structures are being fabricated on the same substrate. The conductor that forms a part of the inductor structure need not be a bond wire, but rather can be another type of conductor. The volume of liquid need not be deposited such that the conductor extends through the volume of liquid. In one example, the volume of liquid is deposited to cover a portion of a signal conductor on a substantially planar substrate, or printed circuit board, integrated circuit chip, or other object. The volume of liquid can be deposited in an indentation, hole or trench. In one example, a signal conductor extends around a peripheral rim of a hole so that the solidified liquid disposed in the hole forms a sort of magnetic core. If wire bonding is used in the assembly of the electronic device, then the depositing of the liquid containing the ferromagnetic particles can occur either prior to wire bonding or after wire bonding. The liquid need not be applied in direct contact with the conductor of the inductor, but rather in some embodiments is deposited in the immediate vicinity of the conductor. The conductor of the inductor may, for example, be covered with a thin insulating layer, and the liquid is deposited on the thin insulating layer. The resulting inductor structure can be a part of a transformer where multiple magnetically coupled conductors extend through the same volume of solidified liquid.
Although certain specific embodiments are described above for instructional purposes, the teachings of this patent document have general applicability and are not limited to the specific embodiments described above. Although the IGBT of the novel combination switch in the example of
Claims
1. An electronic device comprising:
- a Punch Through Insulated Gate Bipolar Transistor (PT IGBT) having a gate, a collector, and an emitter;
- a fast recovery diode; and
- a saturable inductor, wherein the saturable inductor and the fast recovery diode are coupled together in series between the emitter and the collector, wherein the saturable inductor has an unsaturated inductance of at least 200 nH, wherein the saturable inductor has a saturated inductance that is less than the unsaturated inductance, and wherein there is no diode whose anode is directly connected to the emitter and whose cathode is directly connected to the collector.
2. The electronic device of claim 1, further comprising:
- a first lead coupled to the gate;
- a second lead coupled to the collector;
- a third lead coupled to the emitter; and
- a body portion that at least in part contains the PT IGBT, the fast recovery diode and the saturable inductor, wherein the first lead extends from the body portion, wherein the second lead extends from the body portion, and wherein the third lead extends from the body portion.
3. The electronic device of claim 1, further comprising:
- a first lead coupled to the gate;
- a second lead coupled to the collector;
- a third lead coupled to the emitter; and
- an amount of encapsulant that overmolds the PT IGBT, the fast recovery diode and the saturable inductor, wherein the PT IGBT is a first integrated circuit, wherein the fast recovery diode is a second integrated circuit, wherein the first lead extends from the encapsulant, wherein the second lead extends from the encapsulant, and wherein the third lead extends from the encapsulant.
4. The electronic device of claim 2, wherein the saturable inductor includes an amount of ferromagnetic material.
5. The electronic device of claim 2, wherein the saturable inductor comprises a bond wire that extends through a volume of ferromagnetic material, wherein the volume is at least one cubic millimeter.
6. The electronic device of claim 2, wherein the saturable inductor comprises a bond wire that extends through an amount of bonding agent, wherein particles of a ferromagnetic material are suspended in the bonding agent.
7. The electronic device of claim 2, wherein the saturable inductor comprises a conductor that makes at least one turn around an amount of ferromagnetic material.
8. The electronic device of claim 2, wherein the saturable inductor is a toroidal inductor.
9. The electronic device of claim 2, wherein the fast recovery diode has a substantially planar upper surface, and wherein the saturable inductor has a substantially planar surface that is mounted to the substantially planar upper surface of the fast recovery diode.
10. The electronic device of claim 2, wherein the PT IGBT can conduct a maximum continuous collector-to-emitter current from the collector to the emitter, wherein the saturable inductor saturates at a saturation current, and wherein the saturation current is non-zero current that is substantially smaller than the maximum continuous collector-to-emitter current.
11. A packaged electronic device comprising:
- a Punch Through Insulated Gate Bipolar Transistor (PT IGBT) having a gate, a collector, and an emitter, wherein the PT IGBT is a first integrated circuit;
- a diode, wherein the diode is a second integrated circuit;
- a saturable inductor, wherein the saturable inductor and the diode are coupled together in series between the emitter and the collector, wherein the saturable inductor has an unsaturated inductance of at least 200 nH, and wherein the saturable inductor has a saturated inductance that is smaller than the unsaturated inductance;
- a package body portion that contains the PT IGBT, the diode and the saturable inductor;
- a first package terminal coupled to the gate;
- a second package terminal coupled to the collector; and
- a third package terminal coupled to the emitter.
12. The packaged electronic device of claim 11, wherein the first package terminal is wire bonded to the gate of the PT IGBT, wherein the third package terminal is wire bonded to the emitter of the PT IGBT, wherein the second package terminal is an extension of a central heat sink portion, and wherein the PT IGBT and the diode are mounted to the central heat sink portion.
13. The packaged electronic device of claim 11, wherein the saturable inductor includes an amount of ferromagnetic material.
14. The packaged electronic device of claim 11, wherein the PT IGBT can conduct a maximum continuous collector-to-emitter current from the collector to the emitter, wherein the saturable inductor saturates at a saturation current, and wherein the saturation current is non-zero current that is substantially smaller than the maximum continuous collector-to-emitter current.
15. A method comprising:
- providing a saturable inductor and a fast recovery diode in series between an emitter of a Punch Through Insulated Gate Bipolar Transistor (PT IGBT) and a collector of the PT IGBT, wherein the saturable inductor is disposed in an electronic device package along with the PT IGBT and the fast recovery diode, wherein the saturable inductor has an unsaturated inductance of at least 200 nH, and wherein the saturable inductor has a saturated inductance that is smaller than the unsaturated inductance.
16. The method of claim 15, wherein the saturable inductor comes out of saturation when a current flow through the saturable inductor falls below a saturation current level, wherein the saturation current level is less than approximately ten amperes.
17. The method of claim 15, wherein the saturable inductor comprises a bond wire that extends through a volume of ferromagnetic material, and wherein the volume is at least one cubic millimeter.
18. The method of claim 15, wherein the saturable inductor comprises a conductor that makes at least one turn around an amount of ferromagnetic material.
19. A method of manufacture comprising:
- assembling a saturable inductor, a diode, and a Punch Through Insulated Gate Bipolar Transistor (PT IGBT) such that the diode and the saturable inductor are coupled in series between an emitter of the PT IGBT and a collector of the PT IGBT, wherein the saturable inductor has an unsaturated inductance of at least 200 nH, and wherein the saturable inductor has a saturated inductance that is less than the unsaturated inductance; and
- encapsulating the saturable inductor, diode and PT IGBT and thereby forming a packaged electronic device.
20. A packaged electronic device comprising:
- a Punch Through Insulated Gate Bipolar Transistor (PT IGBT) having a gate, a collector, and an emitter;
- a fast recovery diode that can conduct a forward conduction current through the fast recovery diode from an anode of the fast recovery diode to a cathode of the fast recovery diode; and
- means for affecting a rate of change of the forward conduction current, wherein the forward conduction current flows from the emitter and through the fast recovery diode and to the collector, wherein the means affects the rate of change as a function of a magnitude of the forward conduction current, wherein the means affects the rate of change such that in a first earlier amount of time the forward conduction current is falling at a first rate, and such that in a second later amount of time the forward conduction current is falling at a second rate, wherein the first rate is steeper than the second rate, wherein the forward conduction current is greater than a predetermined current level throughout substantially the entire first amount of time, and wherein the forward conduction current is smaller than the predetermined current level throughout substantially the entire second amount of time.
21. The packaged electronic device of claim 20, wherein the means causes the rate of change to be reduced when the forward conduction current is falling and falls below a predetermined current level.
22. The packaged electronic device of claim 20, wherein the means is a saturable inductor structure having an unsaturated inductance of at least 200 nH, and wherein the packaged electronic device further includes an amount of encapsulant that at least in part encapsulates the PT IGBT, the fast recovery diode, and the means.
23. The packaged electronic device of claim 20, wherein the means affects of the rate of change such that at the end of the second amount of time the forward conduction current has reached approximately zero, and wherein the second amount of time immediately follows the first amount of time, and wherein at no time during the first amount of time is the forward conduction current negative.
24. The packaged electronic device of claim 20, wherein the means includes a saturable inductor that comes out of saturation at the end of the first amount of time and at the beginning of the second amount of time.
25. The electronic device of claim 1, wherein the PT IGBT can conduct a maximum continuous current between the collector and the emitter, wherein the saturable inductor saturates at a saturation current, and wherein the saturation current is non-zero current that is substantially smaller than the maximum continuous current.
26. The electronic device of claim 1, wherein the electronic device is part of a switching circuit, and wherein no snubber circuit comprising a resistor and a capacitor is coupled in parallel with the PT IGBT.
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Type: Grant
Filed: Jun 2, 2011
Date of Patent: Oct 17, 2017
Assignee: IXYS Corporation (Milpitas, CA)
Inventors: Kyoung Wook Seok (Milpitas, CA), Joseph James Roosma (Santa Clara, CA)
Primary Examiner: Ajay K Arora
Application Number: 13/134,297
International Classification: H01L 29/66 (20060101); H01L 29/10 (20060101);